1. Field of the Invention
The present invention relates to a keypad assembly for a portable terminal, and more particularly to a keypad assembly for a portable terminal that includes a light guide plate.
2. Description of the Related Art
Generally, a keypad assembly for a conventional portable terminal includes a keypad and a switch substrate. The keypad includes a plate-shaped elastic layer and a plurality of key buttons formed on a first surface of the elastic layer. In the keypad, characters, numbers and symbols are respectively printed on a surface of each key button. The switch substrate has a plurality of switches integrated therewith to provide electric contact as each key button is pushed. In this way, it is possible to convert a depression of the respective key buttons into an electric signal.
A portable terminal has lighting elements for a user to use the keypad even in the dark. A plurality of light emitting diodes and inorganic electro luminescence may be used as the lighting elements. The light emitting diodes are generally arranged on a printed circuit board, while the inorganic electro luminescence is inserted in an elastic pad.
FIG. 1 is a sectional view showing a conventional keypad assembly 100. FIG. 2 is a plan view showing the keypad assembly 100 shown in FIG. 1. The conventional keypad assembly 100 includes a keypad 130, a light guide plate 140, a light source 150, a switch substrate 120 and upper and lower cases 111 and 112. The keypad 130 includes an elastic layer 132 and key buttons 210 formed on the elastic layer 132. The light guide plate 140 is placed under the keypad 130. The light source 150 is disposed at a side of the light guide plate 140 to emit light into the light guide plate 140.
The key buttons 131 may be either integrally formed on the elastic layer 132 or attached to the elastic layer 132 after being formed separately. When a user releases a press to any key button 131 after a key operation, the elastic layer 132 makes the key button 131 recover to an initial state.
The switch substrate 120 includes a dome sheet 121 and a printed circuit board 122. The dome sheet 121 has a plurality of dome switches 123 each of which corresponds to each key button 131. The dome sheet 121 is seated on an upper surface of the printed circuit board 122. The printed circuit board 122 has a plurality of electric contacts each of which can come into contact with each dome switch 123.
The light guide plate 140 has pressing protrusions 142 that are formed on a lower surface thereof to face each dome switch 123. The light guide plate 140 also has reflection patterns 141 that are respectively formed around each pressing protrusion 142 in order to reflect a part of light toward the key buttons 131. A part of the light transmitted in the light guide plate 140 is reflected by means of the reflection patterns 141 toward the key buttons 131, while the rest of the light exits out of the light guide plate 140 to the atmosphere.
However, the light exiting out of the light guide plate illuminates not only the key buttons but also other elements, which causes light loss. Also, this light loss causes the user's eyes to be diverted or distracted to other elements besides the key buttons.